The applicant has isolated a new retina-specific gene which is termed HRG4 (human retinal gene 4). The applicant has shown that HRG4 (1) maps to chromosome 17, (2) is conserved in other species, (3) does not match any known sequence, and (4) is expressed specifically in photoreceptors, particularly in the differentiated state. The fact that autosomal dominant retinitis pigmentosa (ADRP) in a South African family was recently mapped to chromosome 17p and Leber's congenital amaurosis was preliminarily mapped to 17q led the applicant to hypothesize that mutations in HRG4 could cause retina degenerations. The long-range goal is to isolate new human retinal genes such as HRG4 to provide the opportunity to further our understanding of retinal biology and function and to serve as candidate genes for human retina degenerations. To achieve this goal the following aims are proposed: (1) to determine functional aspects of the HRG4 gene product, the applicant will: (a) express the protein, prepare antibodies and immunolocalize HRG4 at the light and electron microscopic levels, (b) determine its developmental expression as well as its daily fluctuations or movements by immunocytochemistry and in situ hybridization in rats, and (c) probe its function at the electroretinogram level in situ in rats and rat retina explants by the use of antibodies and antisense molecules; (2) to complete the analysis of HRG4 at the nucleotide level, the applicant will: (a) determine whether HRG4 is a member of a gene family, (b) clone and characterize the gene, and (c) clone and characterize a rat homologue cDNA for use as a specific functional probe (for some experiments in aim 1); and (3) to analyze the HRG4 gene as a candidate gene for human retinal degenerations, the applicant will: (a) screen for deletions, rearrangements or more subtle mutations using DNA from patients, (b) perform linkage analysis and screening of normal controls on any mutations found in the patients, and (c) sublocalize the HRG4 gene on chromosome 17.